Air bag sealer silicone rubber composition

ABSTRACT

When an air bag is prepared by laying a pair of silicone rubber-impregnated and/or coated base fabric pieces one on the other, with the coated surfaces of the pieces inside, and joining peripheral portions of the pieces together to form a bag, an addition reaction curing type silicone rubber composition which cures into a silicone rubber having an elongation at break of at least 1000% is used as a sealer and applied to the peripheral portions of the base fabric pieces, thereby achieving improved adhesion therebetween.

TECHNICAL FIELD

[0001] This invention relates to a process of preparing an air bag bylaying a pair of base fabric pieces impregnated and/or coated withsilicone rubber one on the other, with the coated surfaces of the piecesinside, and joining peripheral portions of the pieces together to form abag, and more particularly, to a silicone rubber composition for use asa sealer to be applied to the peripheral portions of the base fabricpieces prior to joining.

BACKGROUND OF THE INVENTION

[0002] One typical process for preparing an air bag involves the stepsof furnishing a pair of base fabric pieces impregnated and/or coatedwith silicone rubber, laying the pieces one on the other, with thecoated surfaces of the pieces inside, and bonding or stitchingperipheral portions of the pieces together to form a bag. An attempt hasbeen made to apply an adhesive silicone rubber composition as a sealerto the peripheral portions of the base fabric pieces prior to bonding orstitching. With the state of the art, it is very difficult to bond anuncured silicone rubber composition to once cured silicone rubber.

SUMMARY OF THE INVENTION

[0003] An object of the present invention is to provide, in connectionwith the aforementioned air bag preparation process, a silicone rubbercomposition which is applicable as a sealer to the peripheral portionsof the silicone rubber-coated base fabric pieces prior to bonding orstitching and develops good adherence thereto.

[0004] In connection with a process of preparing an air bag by laying apair of base fabric pieces impregnated and/or coated with siliconerubber one on the other, with the coated surfaces of the pieces inside,and bonding or stitching peripheral portions of the pieces together toform a bag, the present invention provides an addition reaction curingtype silicone rubber composition which cures into a silicone rubberhaving an elongation at break of at least 1000%. Preferably a calciumcarbonate powder is added to the composition. The silicone rubbercomposition is suited for use as a sealer to be applied to theperipheral portions of the base fabric pieces prior to bonding orstitching and develops good adherence to the base fabric pieces.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005]FIG. 1 illustrates an inflation test for adherence evaluationwhere an adhesive silicone rubber composition is applied to a basefabric piece in a pattern to form a bag.

[0006]FIG. 2 illustrates how to inject air into the bag.

DETAILED DESCRIPTION OF THE INVENTION

[0007] The present invention relates to a process for preparing an airbag by furnishing a pair of base fabric pieces impregnated and/or coatedwith silicone rubber, laying the pieces one on the other, with thecoated surfaces of the pieces faced inside, and bonding or stitchingperipheral portions of the pieces together to form a bag. The siliconerubber composition of the present invention is used as a sealer, thatis, applied to the peripheral portions of the base fabric pieces priorto the bonding or stitching step for establishing a firm bond betweenthe peripheral portions after the bonding or stitching step. Thus thebonded or stitched portions are tightly sealed.

[0008] The type of base fabric, the type of silicone rubber compositionaffording the silicone rubber with which the base fabric is impregnatedand/or coated (including curable silicone rubber compositions ofdifferent types, for example, organic peroxide curing type, additionreaction curing type, condensation reaction curing type, and UV curingtype), and the impregnating or coating method (for example, coating,imprinting, screen printing and dipping) may be well-known types ormethods. Namely, any desired base fabric can be impregnated or coatedwith any desired silicone rubber composition by well-known means.

[0009] The air bag sealer silicone rubber composition of the presentinvention is a silicone rubber composition of the addition reactioncuring type which cures into a silicone rubber having an elongation atbreak of at least 1,000%, desirably at least 1,200% and more desirablyat least 1,400%. The upper limit of elongation is usually up to 2,500%,desirably up to 2,000%, though not critical.

[0010] The elongation at break is measured by the following method. Acured silicone rubber sheet of 1 mm thick was punched using a dumbbellcutter according to ASTM D1822L. The dumbbell specimen is marked withgages spaced apart 1 cm. With one end of the dumbbell secured, the otherend is pulled at a constant rate of 300 mm/min until the dumbbellspecimen is broken. A percent elongation at this point is determined.

[0011] A preferred embodiment is an addition reaction curing typesilicone rubber composition comprising (i) an organopolysiloxanecontaining at least two alkenyl radicals in a molecule, (ii) anorganohydrogenpolysiloxane containing at least two silicon atom-bondedhydrogen atoms in a molecule, and (iii) a platinum group metal catalyst.Desirably the composition further contains (iv) an organopolysiloxaneresin having siloxane units containing alkenyl radicals and siloxaneunits of the formula: SiO_(4/2) in a molecule, and more desirably (v) analkoxysilane or a partial hydrolytic condensate thereof. In any of thesepreferred compositions, inclusion of (vi) a calcium carbonate powder isrecommended. These components are described in more detail.

[0012] (i) Alkenyl-Containing Organopolysiloxane

[0013] The alkenyl-containing organopolysiloxane used herein is a basepolymer in the silicone rubber composition and should contain at leasttwo alkenyl radicals in a molecule. Most often, it is a linear one whosebackbone consists essentially of recurring diorganosiloxane units andwhich is blocked with a triorganosiloxy radical at each end of itsmolecular chain. It may contain a branched structure in part in itsmolecular structure or even be cyclic. From the standpoint of mechanicalstrength and other physical properties of the cured product, a lineardiorganopolysiloxane is preferred. The alkenyl radicals may be attachedonly at the ends of the molecular chain or at the ends and intermediatesof the molecular chain. Typically, the alkenyl-containingdiorganopolysiloxane are represented by the general formula (1):

X—SiOR¹ ₂—(SiR¹ ₂O)_(n)—(SiR¹XO)_(m)—SiR¹ ₂—X   (1)

[0014] wherein R¹ is independently a substituted or unsubstitutedmonovalent hydrocarbon radical free of aliphatic unsaturation, X is analkenyl radical, n is 0 or an integer of at least 1, m is 0 or aninteger of at least 1. The unit “m” (SiR¹XO) and the unit “n” (SiR¹ ₂O)are arranged at random.

[0015] Examples of suitable substituted or unsubstituted monovalenthydrocarbon radicals free of aliphatic unsaturation represented by R¹include alkyl radicals such as methyl, ethyl, propyl, isopropyl, butyl,isobutyl, tert-butyl, pentyl, neopentyl, hexyl, heptyl, octyl, nonyl,decyl and dodecyl; cycloalkyl radicals such as cyclopentyl, cyclohexyland cycloheptyl; aryl radicals such as phenyl, tolyl, xylyl, naphthyland biphenylyl; aralkyl radicals such as benzyl, phenylethyl,phenylpropyl and methylbenzyl; and substituted radicals of the foregoingin which some or all of the carbon atom-bonded hydrogen atoms aresubstituted with halogen atoms (e.g., fluoro, chloro, bromo), cyanoradicals or the like, such as chloromethyl, 2-bromoethyl,3-chloropropyl, 3,3,3-trifluoropropyl, chlorophenyl, fluorophenyl,cyanoethyl and 3,3,4,4,5,5,6,6,6-nonafluorohexyl. Those radicals having1 to 10 carbon atoms, especially 1 to 6 carbon atoms are typical. Ofthese, preferred are substituted or unsubstituted alkyl radicals having1 to 3 carbon atoms such as methyl, ethyl, propyl, chloromethyl,bromoethyl, 3,3,3-trifluoropropyl and cyanoethyl and substituted orunsubstituted phenyl radicals such as phenyl, chlorophenyl andfluorophenyl.

[0016] Examples of suitable alkenyl radicals represented by X includethose having about 2 to about 8 carbon atoms such as vinyl, allyl,propenyl, isopropenyl, butenyl, hexenyl and cyclohexenyl, with loweralkenyl radicals such as vinyl and allyl being preferred.

[0017] In formula (1), n is an integer of 0, 1 or greater, m is aninteger of 0, 1 or greater. Preferably n and m are integers satisfying10≦n+m≦10,000, and more preferably 50≦n+m≦2,000 and 0≦m/(n+m)≦0.2.

[0018] These alkenyl-containing diorganopolysiloxanes should preferablyhave a viscosity of 10 to 1,000,000 cSt at 25° C., more preferably 100to 500,000 cSt at 25° C.

[0019] (ii) Organohydrogenpolysiloxane

[0020] The organohydrogenpolysiloxane serves as a crosslinking agent andcontains at least two, preferably at least three hydrogen atoms eachattached to a silicon atom (i.e., SiH radicals) in a molecule. Theorganohydrogenpolysiloxane may have a linear, branched or cyclicstructure or be a resinous one having three-dimensional networkstructure. The upper limit of the number of SiH radicals in one moleculeis usually about 300 or less, preferably about 100 or less, though notcritical. The organohydrogenpolysiloxane desirably has a degree ofpolymerization of about 2 to about 300, more desirably about 3 to about150 (which corresponds to the number of silicon atoms per molecule). Itis noted that the SiH radicals may be positioned at the end or anintermediate of the molecular chain or both.

[0021] Most often, the organohydrogenpolysiloxane (C) is represented bythe following average compositional formula (2).

H_(a)R² _(b)SiO_((4−a−b)/2)   (2)

[0022] In formula (2), R² is independently a substituted orunsubstituted monovalent hydrocarbon radical free of aliphaticunsaturation, “a” and “b” are numbers satisfying 0<a<2, 0.8≦b≦2 and0.8<a+b≦3, preferably 0.01≦a≦1, 1≦b≦2 and 1.01≦a+b≦3, and morepreferably 0.05≦a≦1, 1.5≦b≦2 and 1.8≦a+b≦2.7.

[0023] Examples of suitable substituted or unsubstituted monovalenthydrocarbon radicals free of aliphatic unsaturation represented by R²are as exemplified for R¹ in formula (1). Monovalent hydrocarbonradicals having 1 to 10 carbon atoms, especially 1 to 7 carbon atoms aretypical. Of these, lower alkyl radicals having 1 to 3 carbon atoms suchas methyl and 3,3,3-trifluoropropyl are preferred as well as phenyl.

[0024] Examples of the organohydrogenpolysiloxane include siloxaneoligomers such as 1,1,3,3-tetramethyldisiloxane,1,3,5,7-tetramethyltetracyclosiloxane, and1,3,5,7,8-pentamethylpentacyclosiloxane; both endtrimethylsiloxy-blocked methylhydrogenpolysiloxane, both endtrimethylsiloxy-blocked dimethylsiloxane-methylhydrogensiloxanecopolymers, both end silanol-blocked methylhydrogenpolysiloxane, bothend silanol-blocked dimethylsiloxane-methylhydrogensiloxane copolymers,both end dimethylhydrogensiloxy-blocked dimethylpolysiloxane, both enddimethylhydrogensiloxy-blocked methylhydrogenpolysiloxane, both enddimethylhydrogensiloxy-blocked dimethylsiloxane-methylhydrogensiloxanecopolymers; and silicone resins comprising R₂(H)SiO_(1/2) units andSiO_(4/2) units and optionally, RSiO_(3/2) units, R₂SiO_(2/2) units,R(H)SiO_(2/2) units, (H)SiO_(3/2) units or RSiO_(3/2) units wherein R isa substituted or unsubstituted monovalent hydrocarbon radical asexemplified above for R¹. Also included are those represented by thefollowing formulae.

[0025] n is an integer of 1 to 50.

[0026] n is an integer of 0 to 40,

[0027] m is an integer of 2 to 40,

[0028] m+n=2 to 80.

[0029] The unit “m” (Osi) and the unit “n” (Osi) are arranged at random.

[0030] The organohydrogenpolysiloxane used herein can be prepared bywell-known methods, for example, by co-hydrolyzing at least onechlorosilane selected from the general formulae: R²SiHCl₂ and R² ₂SiHClwherein R² is as defined above, or by co-hydrolyzing a mixture of theforegoing chlorosilane and at least one chlorosilane selected from thegeneral formulae: R² ₃SiCl and R² ₂SiCl₂ wherein R² is as defined above.If desired, the polysiloxane resulting from such cohydrolysis is furthersubjected to equilibration reaction, resulting in anorganohydrogenpolysiloxane which is also useful.

[0031] Component (ii) is preferably used in such amounts that 0.5 to 4moles, more preferably 0.8 to 2.5 moles of silicon atom-bonded hydrogenatoms (i.e., SiH radicals) in the organohydrogenpolysiloxane (ii) arepresent per mole of alkenyl radicals in the alkenyl-containingorganopolysiloxane (i) or in components (i) and (iv) combined ifcomponent (iv) to be described later has alkenyl radicals such as vinyl.

[0032] (iii) Platinum Group Metal Catalyst

[0033] The platinum group metal catalyst used herein is a catalyst forpromoting the addition reaction between alkenyl groups in component (i)and silicon atom-bonded hydrogen atoms in component (ii). Well-knowncatalysts used in hydrosilylation reaction are useful. Exemplarycatalysts are platinum, palladium and rhodium base catalysts includingelemental platinum group metals such as platinum (inclusive of platinumblack), rhodium and palladium; platinum chloride, chloroplatinic acidand chloroplatinic acid salts such as H₂PtCl₄.nH₂O, H₂PtCl₆.nH₂O,NaHPtCl₆.nH₂O, KHPtCl₆.nH₂O, Na₂PtCl₆.nH₂O, K₂PtCl₄.nH₂O, PtCl₄.nH₂O,PtCl₂ and Na₂HPtCl₄.nH₂O wherein n is an integer of 0 to 6, preferably 0or 6; alcohol-modified chloroplatinic acid (see U.S. Pat. No.3,220,972); complexes of chloroplatinic acid with olefins (see U.S. Pat.No. 3,159,601, 3,159,662 and 3,775,452); platinum group metals such asplatinum black and palladium on carriers such as alumina, silica andcarbon; rhodium-olefin complexes; chlorotris (triphenylphosphine)rhodium (known as Wilkinson catalyst); and complexes of platinumchloride, chloroplatinic acid or chloroplatinic acid salts withvinyl-containing siloxanes, especially vinyl-containing cyclicsiloxanes.

[0034] The catalyst (iii) is used in a catalytic amount, typically about0.1 to 1,000 parts, preferably about 0.1 to 500 parts, and morepreferably about 0.5 to 200 parts by weight of platinum group metal permillion parts by weight of components (i) and (ii) combined.

[0035] (iv) Organopolysiloxane Resin

[0036] Preferably, an organopolysiloxane resin is added to the siliconerubber composition. It is an organopolysiloxane resin ofthree-dimensional network structure containing essentially branchedunits represented by SiO₂ units and/or RSiO_(3/2) units, and optionally,R₃SiO_(1/2) units and/or R₂SiO units wherein R is a monovalenthydrocarbon radical such as alkyl, alkenyl or aryl. Inclusion of thisorganopolysiloxane resin increases the strength of silicone rubber.Exemplary organopolysiloxane resins are resins consisting of(CH₃)₃SiO_(1/2) units and SiO_(4/2) units, resins consisting of(CH₃)₃SiO_(1/2) units, (CH₂═CH)(CH₃)₂SiO_(1/2) units and SiO₂ units,resins consisting of (CH₃)₃SiO_(1/2) units, (CH₂═CH)SiO_(3/2) units andSiO_(4/2) units, resins consisting of (CH₂═CH)(CH₃)₂SiO_(1/2) units andSiO_(4/2) units, and resins consisting of (CH₂═CH)(CH₃)₂SiO_(1/2) units,(CH₂═CH)SiO_(3/2) units and SiO_(4/2) units. In particular, those resinshaving alkenyl radicals, typically vinyl are effective for improving thestrength of the compositions when they are incorporated into thecrosslinked structure.

[0037] The organopolysiloxane resin (iv) is preferably blended inamounts of about 0.01 to 30 parts by weight, more preferably about 0.1to 15 parts by weight per 100 parts by weight of the alkenyl-containingorganopolysiloxane (i).

[0038] (v) Alkoxysilane or Partial Hydrolytic Condensate

[0039] Suitable alkoxysilanes and partial hydrolytic condensates thereofare tetrafunctional alkoxysilanes including tetraalkoxysilanes such astetramethoxysilane and tetraethoxysilane; and trifunctionalalkoxysilanes including organotrialkoxysilanes, typicallyalkyltrialkoxysilanes, alkenyltrialkoxysilanes and aryltrialkoxysilanessuch as methyltrimethoxysilane, methyltriethoxysilane,ethyltrimethoxysilane, vinyltrimethoxysilane, phenyltrimethoxysilane,and methyltri(methoxyethoxy)silane, and alkoxysilanes having epoxy oramino-containing substituent groups such asγ-glycidoxypropyltrialkoxysilanes and γ-aminopropyltriethoxysilane, andpartial hydrolytic condensates of the foregoing. They may be used aloneor in admixture of two or more.

[0040] The alkoxysilane or partial hydrolytic condensate thereof (v) ispreferably blended in amounts of about 0.1 to 10 parts by weight, morepreferably about 0.5 to 5 parts by weight per 100 parts by weight ofcomponent (i).

[0041] (vi) Calcium Carbonate Powder

[0042] Calcium carbonate (CaCO₃) powder is preferably blended in theinventive silicone rubber composition because the silicone rubber isimproved in elongation at break and adherence.

[0043] The calcium carbonate powder used herein may be selected fromwell-known ones such as heavy calcium carbonate (i.e., calcium carbonatefine powder obtained by wet or dry pulverizing method.) and colloidalcalcium carbonate (i.e., calcium carbonate fine powder obtained bysedimentation method.). It may or may not be surface treated with resinsor fatty acids. From the standpoints of fluidity and reinforcement,calcium carbonate powder having an average particle size of 0.01 to 50μm, preferably 0.02 to 50 μm, more preferably 0.03 to 10 μm. The averageparticle size is determined as a weight average value D₅₀ or mediandiameter in particle size distribution measurement by the laser lightdiffraction method.

[0044] The calcium carbonate powder generally retains some moisture.Moisture may be removed if desired. Moisture removal is carried out, forexample, by mixing a dimethylpolysiloxane with calcium carbonate powderand heat treating the mixture. The heating temperature is usually 50° C.or higher, preferably 80 to 200° C., and a reduced pressure may beemployed for promoting the heat treatment. By this heat treatment, thecalcium carbonate powder which has not been surface treated issubstantially treated with the dimethylpolysiloxane whereby the moistureis released. When the addition reaction curing type silicone rubbercomposition is loaded with such dry calcium carbonate powder, thecomposition can be stabilized without chemically altering theorganohydrogenpolysiloxane (ii).

[0045] The calcium carbonate powder (vi) is preferably blended inamounts of about 0.01 to 100 parts by weight, more preferably about 0.1to 50 parts by weight per 100 parts by weight of component (i).

[0046] Other Components

[0047] In addition to the above-described components (i) to (vi), theremay be added to the inventive composition reinforcing inorganic fillerssuch as fumed silica and fumed titanium dioxide; reinforcing siliconeresins; and non-reinforcing inorganic fillers such as calcium silicate,titanium dioxide, ferric oxide, and carbon black. These inorganicfillers are generally used in amounts of 0 to 200 parts by weight per100 parts by weight of all the components excluding the inorganicfillers. It is also acceptable to add organic titanium compounds such astitanium chelates and organic titanic acid esters. The organic titaniumcompounds are generally used in amounts of 0 to 10 parts by weight,preferably 0.1 to 5 parts by weight per 100 parts by weight of all thecomponents excluding the inorganic fillers.

[0048] Curable Silicone Rubber Composition and Cured Product

[0049] Like conventional curable silicone rubber compositions, theinventive composition may be formulated as a two part compositionwherein two parts are kept separate and on use, mixed together forcuring. Independent of whether the inventive composition is one parttype or two part type, an epoxy radical-containing polysiloxane compoundor ester siloxane compound may be additionally included in thecomposition if desired for improving the adhesion of the composition.The resulting composition is also improved in flow.

[0050] Under the same conditions as used for well-known additionreaction curing type silicone rubber compositions, the inventivecomposition can be cured. For example, the inventive composition curessatisfactorily at room temperature, but can be heated for curing ifdesired.

EXAMPLE

[0051] Examples of the invention are given below by way of illustrationand not by way of limitation.

Examples 1-4 & Comparative Examples 1-2

[0052] Using the components described below, silicone rubbercompositions of the formulation shown in Table 1 were prepared. Thecompositions were evaluated by several tests, with the results shown inTable 1.

[0053] Components

[0054] (A-1) Untreated calcium carbonate Whiton SSB by Shiraishi KogyoCo., Ltd., average particle size 1.5 μm

[0055] (A-2) Surface treated calcium carbonate Calex 300 by MaruoCalcium Co., Ltd. average particle size 0.04 μm surface treating agent:higher fatty acid (a mixture of lauric acid, myristic acid, palmiticacid, oleic acid and stearic acid)

[0056] (B) Organopolysiloxane Vinyl-containing linear organopolysiloxanerepresented by the formula:

[0057] wherein Me is methyl, Vi is vinyl, and n is such a number thatthe siloxane has a viscosity of 100,000 cSt at 25° C.

[0058] (C-1) Organohydrogenpolysiloxane

[0059] (C-2) Organohydrogenpolysiloxane

[0060] (D) Platinum group metal catalystplatinum-divinyltetramethyldisiloxane complex in toluene (Pt content 0.5wt %)

[0061] (E) Reinforcing resin vinyl-containing methylpolysiloxane resincomposed of Vi(Me)₂SiO_(1/2) units and SiO_(4/2) units

[0062] (F) Alkoxysilane or partial hydrolytic condensatephenyltrimethoxysilane KBM103 by Shin-Etsu Chemical Co., Ltd.

[0063] (G) Reinforcing inorganic filler fumed silica treated withdimethylpolysiloxane and hexamethyldisilazane

[0064] (H) Cure controlling agent 50% ethynyl cyclohexanol in toluene

[0065] (I) Organotitanium Ti[OCH₂CH(C₂H₅)(CH₂)₃CH₃]₄

[0066] Runs were carried out using the foregoing components. Components(A) and (B) were mixed. The mixture was heat treated at 150° C. for 2hours under a reduced pressure. After cooling to room temperature, themixture was compounded with components (C), (D), (E), (F), (G), (H) and(I) under a reduced pressure, yielding an adhesive silicone rubbercomposition.

[0067] Tests

[0068] Peel Test and Cohesive Failure:

[0069] Two fabric pieces coated with silicone rubber were matedtogether, with the coated surfaces faced inside. At this point, theadhesive silicone rubber composition was applied therebetween to athickness of 0.5 mm. After the silicone rubber composition was cured,the fabric pieces were peeled apart using a testing machine Strograph(Toyo Seiki Seisaku-sho, Ltd.). A peel adhesion strength (N/cm) wasmeasured and a percent cohesive failure at the adhesion interface wascomputed.

[0070] Elongation at Break:

[0071] The adhesive silicone rubber composition was cured into asilicone rubber sheet of 1 mm thick, which was punched using a dumbbellcutter according to ASTM D1822L. The dumbbell specimen was marked withgages spaced apart 1 cm. With one end of the dumbbell secured, the otherend was pulled at a constant rate of 300 mm/min until the dumbbellspecimen was broken. A percent elongation at break was determined.

[0072] Inflation Test Adhesion:

[0073] A test was carried out according to the actual usage of an airbag. Fabric pieces surface coated with silicone rubber were furnished.On the rubber-coated surface of one fabric piece, the uncured adhesivesilicone rubber composition I was applied in the hatched pattern shownin FIG. 1. The other fabric piece was laid thereon, with therubber-coated surface faced inside. The assembly was held at 23° C. forone day for curing whereby the fabric pieces were joined to form a bag.Air under 7 atmospheres was injected into the bag for 0.5 second fromthe open end as shown by the arrow in FIG. 2. The bonded state of theadhesive silicone rubber composition was observed. It was rated OK whencohesive failure occurred, and NG when interfacial peeling occurred. Itis understood that FIGS. 1 and 2 are plan views of an air bag as viewedfrom above. TABLE 1 Comparative Components Example Example (pbw) 1 2 1 23 4 A-1 0 0 35 25 20 0 A-2 0 0 0 0 0 20 B 94 94 94 94 94 94 C-1 1.9 1.91.9 1.9 1.9 1.9 C-2 8.7 8.7 8.7 8.7 8.7 8.7 D 0.5 0.5 0.5 0.5 0.5 0.5 E7.5 7.5 7.5 7.5 7.5 7.5 F 1 1 1 1 1 1 G 21 30 21 21 21 21 H 0 0 0.150.15 0.15 0.15 I 0.5 0.5 0.5 0.5 0.5 0.5 Peel strength (N/cm) 2.0 2.76.0 6.3 4.7 5.0 Cohesive failure 20 80 100 100 100 100 (%) Elongation at800 850 1100 1300 1400 1450 break (%) Inflation test NG NG OK OK OK OKadhesion

[0074] In Comparative Examples 1 and 2, calcium carbonate was not added.Comparative Example 1 contained a less amount of the reinforcinginorganic filler than Comparative Example 2. Comparative Example 2containing a more amount of the reinforcing inorganic filler developedbetter adhesion than Comparative Example 1, but not to a satisfactoryextent.

[0075] Examples 1 to 3 contained different amounts of untreated calciumcarbonate, which gave satisfactory results including a cohesive failureof 100%. Satisfactory adhesion was developed even when the amount ofcalcium carbonate was reduced. Examples 3 and 4 contained the sameamount of untreated calcium carbonate and treated calcium carbonate,respectively. No difference in adhesion was found whether the calciumcarbonate had been treated or not.

[0076] When silicone rubber-impregnated and/or coated fabric pieces aremated, with their coated surfaces inside, and joined along a peripheryto form a bag, the adhesive silicone rubber compositions of Exampleshaving surface-treated or untreated calcium carbonate added thereto areused as a sealer where the peripheral portions of the fabric pieces arejoined together whereby an improved bond is established between theperipheral portions of the fabric pieces.

[0077] In an air bag prepared by laying a pair of base fabric piecesimpregnated and/or coated with silicone rubber one on the other, withthe coated surfaces of the pieces inside, and bonding or stitchingperipheral portions of the pieces together to form a bag, the siliconerubber composition of the invention is used as a sealer and applied tothe peripheral portions of the base fabric pieces, thereby achievingimproved adhesion therebetween.

[0078] Japanese Patent Application No. 2002-053973 is incorporatedherein by reference.

[0079] Reasonable modifications and variations are possible from theforegoing disclosure without departing from either the spirit or scopeof the present invention as defined by the claims.

1. In connection with a process of preparing an air bag by laying a pairof base fabric pieces impregnated and/or coated with silicone rubber oneon the other, with the coated surfaces of the pieces inside, and bondingor stitching peripheral portions of the pieces together to form a bag,an addition reaction curing type silicone rubber composition for use asa sealer to be applied to the peripheral portions of the base fabricpieces prior to bonding or stitching, the composition curing into asilicone rubber having an elongation at break of at least 1000%.
 2. Thecomposition of claim 1, further comprising calcium carbonate powder. 3.The composition of claim 2 wherein the calcium carbonate powder has beensurface treated.
 4. The composition of claim 2 wherein the calciumcarbonate powder has an average particle size of 0.01 to 50 μm.
 5. Thecomposition of claim 1 wherein the addition reaction curing typesilicone rubber composition comprises (i) an organopolysiloxanecontaining at least two alkenyl radicals in a molecule, (ii) anorganohydrogenpolysiloxane containing at least two silicon atom-bondedhydrogen atoms in a molecule, (iii) a platinum group metal catalyst, and(iv) an organopolysiloxane resin having siloxane units containingalkenyl radicals and siloxane units of the formula: SiO_(4/2) in amolecule.
 6. The composition of claim 5, further comprising analkoxysilane or a partial hydrolytic condensate thereof.